Hierarchy of Storage devices, Short Services of OS, Short note on types of OS

1. PREPAREDBY: MOMINA IDREES 1
QUESTION NO # 1
Write down hierarchy of storage devices?
STORAGE DEVICE HIERARCHY
“A storage device hierarchy consists of a group of storage devices that have different costs for
storing data, different amounts of data stored, and different speeds of accessing the data.”
Storage hierarchy systems are a means of two or more types of storage “cost objectives and
functional requirements (performance)”; ratio (cost / performance) of storage components by
combining elements with different characteristics to meet the needs of a given class of
applications. In general, the process involves the organization of data on fast and slower devices
into manageable units and by transferring the most frequently used data to the faster device on a
dynamic basis. The purpose is to increase the overall functional effectiveness of a computing
system.
Fig. STORAGE DEVICE HIERARCHY

2. PREPAREDBY: MOMINA IDREES 2
QUESTION NO # 2
Write down short note on services of OS?
SERVICES OF OPERATING SYSTEM
Following are a few common services provided by an operating system −
 Program execution
o Loads a program into memory and execute it.
o Provides a mechanism for process synchronization, communication and deadlock
handling.
 I/O operations
o I/O operation means read or write operation with any file or any specific I/O
device.

3. PREPAREDBY: MOMINA IDREES 3
 File System manipulation
o The operating system gives the permission to the program for operation on file.
o OS provides an interface to the user to create/delete files/directories.
o To create the backup of file system.
 Communication
o Two processes often require data to be transferred between them.
o Communication may be implemented by two methods, either by Shared Memory
or by Message Passing.
 Error Detection
o The OS constantly checks for possible errors and takes an appropriate action to
ensure correct and consistent computing.
 Resource Allocation
o The OS manages all kinds of resources using schedulers. CPU scheduling
algorithms are used for better utilization of CPU.
 Protection
o The OS provides authentication features for each user by means of passwords.

4. PREPAREDBY: MOMINA IDREES 4
QUESTION NO # 3
Short note on following:
a) EMBEDDED OPERATING SYSTEM:
“An embedded operating system is a specialized OS for use in the computers built into
larger systems.”
Characteristics and Applications:
 These operating systems are typically found in standalone computerized equipment such
as ATM machines or navigation systems.
 Such a system typically runs a specific piece of programming, such as the guidance system
on a rocket, and nothing else.
 Many real-time operating systems are also embedded. This type of system requires
immediate response to data input—latency and lag are not an option.
 Typically run immediate response procedures, such as the anti-lock breaking processes on
a car.
Classification of Embedded Systems
 Stand-alone Embedded Systems
o As the name implies, stand-alone systems work in stand-alone mode. They
take inputs, process them and produce the desired output. Used in process
control, automobiles, consumer electronic items etc. fall into this category.
 Real-time Embedded Systems
o Embedded systems in which some specific work has to be done in a specific
time period are called real-time systems.

5. PREPAREDBY: MOMINA IDREES 5
 Networked Information Appliances
o Embedded systems that are provided with network interfaces and accessed by
networks such as Local Area Network or the Internet are called networked
information appliances. These systems run the protocol TCP/IP stack and get
connected through Ethernet to an network and communicate with other nodes
in the network.
 Mobile Devices
o Mobile devices such as mobile phones, Personal Digital Assistants (PDAs),
smart phones etc. are a special category of embedded systems.
Problems:
 Many embedded systems do not operate in a controlled environment.
 Excessive heat is often a problem, especially in applications involving combustion
(e.g., many transportation applications).
 The cycle time between identification of a product opportunity and product deployment
(also called Time to Market) can be quite long for embedded systems.
b) MONOLITHIC:
“A monolithic kernel is an operating system architecture where the entire operating
system is working in kernel space and is alone in supervisor mode. The monolithic model
differs from other operating system architectures in that it alone defines a high-level
virtual interface over computer hardware.”
Properties:
 Any module can call any other module without any reservation.
 Applications run in non-privileges processor mode.
 It doesn’t enforce data hidings in OS.

6. PREPAREDBY: MOMINA IDREES 6
c) RTOS (RealTime Operating System):
“A real-time system is defined as a data processing system in which the time interval
required to process and respond to inputs is so small that it controls the environment.”
The time taken by the system to respond to an input and display of required updated
information is termed as the response time.
Working:
 Real-time systems are used when there are rigid time requirements on the operation of
a processor
 The flow of data and real-time systems can be used as a control device in a dedicated
application.

7. PREPAREDBY: MOMINA IDREES 7
 A RTOS must have well-defined, fixed time constraints, otherwise the system will
fail. For example, industrial control systems, weapon systems, robots, air traffic
control systems etc.
Types:
 Hard real-time systems
Hard real-time systems guarantee that critical tasks complete on time. In hard real-
time systems, secondary storage is limited or missing and the data is stored in
ROM. In these systems, virtual memory is almost never found.
 Soft real-time systems
Soft real-time systems are less restrictive. Soft real-time systems have limited
utility than hard real-time systems. For example, multimedia, Advanced Scientific
Projects like undersea exploration and planetary rovers, etc.
Problems:
 Can be Costly.
 Thread priority is not good as RTOS do less switching of tasks.
 RTOS are generally complicated and can consume a non-trivial amount of processor
cycles.
d) BATCH OPERATING SYSTEM:
“Batch processing is the execution of a series of jobs in a program on a computer without
manual intervention.”
Working:
 The users of a batch operating system do not interact with the computer directly.
 Each user prepares his job on an off-line device like punch cards and submits it to the
computer operator.
 To speed up processing, jobs with similar needs are batched together and run as a
group.
 The programmers leave their programs with the operator and the operator then sorts
the programs with similar requirements into batches.
Problems:

8. PREPAREDBY: MOMINA IDREES 8
 Lack of interaction between the user and the job.
 CPU is often idle, because the speed of the mechanical I/O devices is slower than the CPU.
 Difficult to provide the desired priority.